"Suspicious driving" may be lame words used for a lawful stop. Traffic violations are not crimes and rules for each are different for stopping and doing an investigation. Violations never need what a crime needs (probable cause) to stop and investigate. Violations only need reasonable suspicion or in Oregon that was redefined as the officer has sufficient grounds to believe a violation may have occurred. That is a really low bar to get over to make a stop.
Without writing a book, what Blume says he was doing met that bar easy. He was driving a vehicle on a public road in a manor consist with serious issues. DUII, DUI, sleepy driver, distracted driver or a driver having a medical emergency at any time of day or night. The officer did what he was paid to do. Blume was driving under the speed limit, 10 or more under is a major clue for being impaired. Swerving within a lane is another problem that each of the 6 things I listed people do.
In his case the officer understood Blume was none of the above, just adjusting/reading his GPS. He would never know unless he stopped Blume. In his case he could have been cited for careless driving (Oregon). If the officer could show other traffic, persons or property was at risk. It does not sound like that was present and no ticket was issued.
Many may not want police to stop drivers for "suspicious driving" but YOU and your families, if you travel on a public roadway are much safer when officers are willing to check drivers doing what he described. Just look up how many innocent people are killed or hurt yearly from drivers that fall into the categories that I listed.